A cancer-killing virus may shrink melanomas in people, according to new results from an ongoing clinical trial presented at the 2013 European Cancer Congress in Amsterdam, Netherlands. The virus—called talimogene laherparepvec or T-VEC—is injected into tumors, where it divides until the cells pop. The phase III trial has more than 400 people with melanoma; T-VEC shrank tumors in nearly one-third of them. Moreover, tumors didn't grow again for at least 9 months in two-thirds of those who responded to the virus. That said, 26% of those treated with T-VEC had serious side effects including fevers and bacterial skin infections.